WO2007116022A2

WO2007116022A2 - Device as well as apparatus and method for the treatment of materials at elevated temperature and under movement and under vacuum

Info

Publication number: WO2007116022A2
Application number: PCT/EP2007/053385
Authority: WO
Inventors: Rüdiger FREDL; Hans Schnell
Original assignee: Ohl Engineering Gmbh Pet Recycling Technologies
Priority date: 2006-04-07
Filing date: 2007-04-05
Publication date: 2007-10-18
Also published as: WO2007116022A3; EP2004376A2

Abstract

The present invention concerns a method and an apparatus for drying and/or thermal treatment of granular or particulate plastic material with a vacuum dryer (1) and a corresponding vacuum dryer with a gas-tight sealable chamber (41) for the plastic material and a rotary axis (2) for rotating or swivelling the chamber, in which the jacket of the chamber is formed as one wall. The apparatus is characterised by the fact that a heating and/or a cooling vessel (10, 11) are arranged upstream and/or downstream of the vacuum dryer (1), such that, in the method, in a first step, pre-heated plastic material is charged in the absence of air into a vacuum-tight or gas-tight sealable chamber of the vacuum dryer, or non-pre- heated plastic material is charged into a vacuum-tight or gas-tight sealable chamber of the vacuum dryer and, after evacuation of the vacuum dryer, is heated by in-feeding and/or through-feeding of an inert hot gas and then can be through- mixed in a second step by movement of the vacuum dryer (1).

Description

Device as well as apparatus and method for the treatment of materials at elevated temperature and under movement and under vacuum Technical field

[0001] The present invention concerns a device or a vacuum dryer for the drying and/or thermal treatment of granular or particulate material, especially plastic, under essentially a vacuum at elevated temperatures and movement or through-mixing of the material as well as an apparatus with such a vacuum dryer and a method for drying and/or thermal treatment of granular or particulate plastic material.

Prior art

[0002] Vacuum tumbling dryers or double cone dryers with vacuum working area are long-established for the drying and post-condensation of granular goods at elevated temperatures. Such vacuum, tumbling or double cone dryers, generally called vacuum dryers, are usually composed of a double-jacketed housing, which surrounds the chamber for the bulk or ground material to be dried. Into the cavity of the double-walled jacket is fed a heat transfer medium, which has been heated outside the dryer. Via this so-called heating or double jacket the goods charged in the dryer can be brought to the temperature necessary for drying and/or thermal treatment. For example, such a vacuum tumbling dryer is used in the recycling of polyethylene terephthalate (PET), as described for example in WO 2004/106025 A1. Here, a corresponding vacuum tumbling dryer is used for the post-condensation of the recycled PET at temperatures of 200D?C to 250D?C and a pressure < 1 mbar with retention times of 4 to 18 hours for the post-condensation stage.

[0003] Although very good results are obtained thereby and the use of batch-wise chargeable vacuum tumbling dryers or double cone dryers, relative to that of continuous in-line installations, which have a continuous throughput of material to be treated, is preferable because defined and understandable treatment parameters can be set for all of the material to be treated since there is no scatter of retention time relative to in-line installations, the time requirement for treatment in the vacuum tumbling dryer for economic application is capable of being increased.

[0004] There have therefore already been attempts to improve the drying process in vacuum tumbling dryers. An example is provided in patent application CH 429597, in which a vacuum tumbling dryer is described in which, by means of direct removal and/or feeding of liquid, solid or gaseous materials, such as filtrate, detergent, solvent etc., treatment in a vacuum tumbling dryer is improved during operation.

Representation of the invention

Technical object

[0005] The object of the present invention is to provide a device or a vacuum dryer or a corresponding apparatus, with which treatment of grainy, granular or particulate goods, such as especially plastic materials, can be improved. Especially, the retention time in the vacuum dryer is to be reduced, for example, for the recycling of PET, with the goal at the same time of being able to set defined treatment parameters that are understandable for all of the treated material.

Technical solution

[0006] This object is achieved with a device having the characteristics of claim 1 as well as an apparatus having the characteristics of claim 10 and a method having the characteristics of claim 18. Advantageous arrangements are the subject of the dependent claims.

[0007] The invention starts out from the realization that heating and/or cooling of the granular or particulate material in the aforementioned dryers requires a substantial amount of time, which offers great potential for time saving. Accordingly, the inventors have found a way here to improve treatment in corresponding dryers.

[0008] From a first aspect, they assume that heating the material to be treated via a heating or a double jacket is relatively ineffective, so that a proposal is made to effect heating by through-feeding corresponding gaseous heating media, for example, inert gases, especially nitrogen, argon and the like. In this way, the heating medium comes into immediate, direct contact with the goods to be heated and heat transfer can take place faster. Accordingly, in the inventive device, the complex design of a double- jacketed housing can also be eschewed. Rather, a single-jacketed housing is sufficient, a fact which brings additional economic advantages.

[0009] From a further aspect, for which protection is likewise sought independently, a corresponding device, i.e. a dryer and the associated method, can be arranged such that already pre-heated material is charged into the movable chamber of the device, whereby, for the purpose of avoiding undesirable reactions of the material to be treated, this takes place under inert gas atmosphere or essentially vacuum conditions, that is, in the pressure range < 1 mbar. Accordingly, from this aspect of the invention, the device must be provided with means for vacuum-tight or gas-tight coupling to supply lines or transfer containers at the charge opening(s). In this way, the entire time-consuming heating step in the dryer is dispensed with. This is especially advantageous if the material already has a certain temperature from a preceding process step, such as is the case for recycling of PET after the crystallization step.

[0010] Where this is not the case, or in order to be able to compensate for fluctuations in the process cycle, it is advantageous to connect a corresponding heating vessel upstream of the device, such that the heating process takes place in the heating vessel and the movable heating chamber is not blocked by the heating periods. In a similar way, a cooling vessel can be connected downstream of the dryer in order that the cooling phase may not have to be performed in the dryer itself, but rather in the cooling vessel. As a result, the various processes, such as heating and/or cooling on one hand and through-mixing on the other are performed in different devices and thus throughput through the vacuum dryer can be increased. In addition, the vacuum dryer can be manufactured more favourably and more simply by eschewing corresponding heat transfer systems. Especially, it is no longer necessary to provide complex heating jackets with double-jacketed housing design, but rather the device or the vacuum dryer can be formed so as to have one wall. Temperature losses during mixing in the vacuum dryer can be compensated with less powerful heaters, for example electrical heaters. Especially, simple heating mats can be provided at the external surface of the vacuum dryer, or the vacuum dryer can be formed such that these may be arranged at its exterior. In this way, the outlay for the manufacture of the vacuum dryer is markedly reduced overall.

[0011] Preferably, the heating and cooling processes in the heating vessel and/or cooling vessel before and/or after the vacuum dryer are also performed such that gaseous heating and/or cooling media are transported through the heating and/or cooling vessels in order that good and effective heat transfer may be assured in direct contact with the goods to be heated and/or cooled.

[0012] Since inert gases, such as nitrogen, argon and the like, are normally used as heating and/or cooling media, it is advantageous to transport these in a loop in order that they may be fed again to the heating or cooling vessel after leaving the heating or cooling vessel after corresponding heating or cooling. Accordingly, the inventive apparatus preferably has heating devices, cooling devices and/or heat exchangers in the loops of the heating or cooling media in order that the heating or cooling media may accordingly be heated or cooled.

[0013] In a preferred embodiment, the heat of the material to be treated that is released during cooling is used simultaneously to heat the material to be treated. This can be accomplished, for example, by providing heat exchanger devices in which the material already treated and the material still to be treated are transported past each other. However, in a simple arrangement, the cooling and/or heating medium from the one loop of the first heating and/or cooling vessel can also be transported past the cooling and/or heating medium from the other loop of the second heating or cooling vessel in a heat exchanger in order that heat transfer and heat recovery may be accomplished in this way. This advantageous embodiment thus additionally offers a substantial potential for energy saving. The heat transfer can take place here from solid to solid, from solid to liquid, solid to gas or liquid to gas and vice versa in each case. The temperatures during treatment in the dryer are usually above ambient, especially above 50⁰C, preferably above 100⁰C and most preferably above 150⁰C, with the chamber preferably greater than 1 m³, especially greater than 10 m³.

Brief description of the drawings

[0014] Further advantages, characteristics and features of the present invention are apparent from the following details description of embodiments using the enclosed drawings. The drawings show in purely schematic form:

[0015] Fig. 1 a schematic diagram of a first inventive apparatus; and in

[0016] Fig. 2 an overview of a second inventive apparatus.

Way(s) to execute the invention

[0017] Fig. 1 is a schematic diagram of an apparatus with a vacuum dryer 1 , an upstream heating vessel 10 and a downstream cooling vessel 11.

[0018] The vacuum dryer 1 has a double-cone shape, with the external jacket of the chamber 41 formed as one wall.

[0019] In the central area, that is, at the seam of the two cone halves is provided a rotary axis 2 with bearing points, about which the chamber 41 can be rotated, such that the plastic particles or the granules inside are mixed.

[0020] In the embodiment shown in Fig. 1 , upstream of the vacuum dryer 1 is a heating vessel 10, which has a charge opening 12 and a discharge opening 13, which may both be sealed vacuum-tight or gas-tight. Furthermore, at the heating vessel 10, which is likewise implemented as one wall, gas inlets and/or outlets 24, 25 and 35 are provided.

[0021] The gas inlet 25 as well as the gas outlet 24 are part of a line loop 16, through which gas can be pumped through the heating vessel 10.

[0022] In addition to the shut-off valves 21 and 22 in the line loop 16 is provided a pumping device 19 as well as a heating device 18, which are connected by a line 23. Furthermore, a gas inlet 20 is likewise provided with a shut-off valve, through which fresh gas can be supplied. The gas, which is pumped in the line loop 16, is usually inert gas, for example nitrogen. However, other inert gases, for example argon or the like can be used for this. If suitable, normal or treated air can also serve as gas.

[0023] The gas pumped in the line loop 16 serves to heat the plastic granules provided in the heating vessel 10, with the gas, which is removed from the heating vessel 10, being heated in the heating device 18, pumped via the pumping device 19 through the line 23 and injected at the gas inlet opening 25 of the heating vessel into the lower region of the heating vessel 10 where it is transported through the loosely piled bulk or ground material of plastic particles or plastic granules, such that this is heated by heat transfer from the heated gas to the plastic particles.

[0024] The inert gas can be exhausted from the heating vessel 10 through the gas exhaust opening 35, to which is likewise assigned a shut-off valve 36. For this purpose, lines 7 as well as a pumping unit 9 are provided. Preferably, the same pumping unit and partly the same lines 7 are used for this purpose which are also attached to the vacuum dryer 1.

[0025] Additionally, the heating vessel 10 has a valve opening 42, with which the heating vessel 10 can be vented.

[0026] In addition to the heating vessel 10, which is upstream of the vacuum dryer 1 , the preferred embodiment of the inventive apparatus in Fig. 1 has a cooling vessel 11 , which is downstream of the vacuum dryer 1. The cooling vessel 11 is constructed in similar way as the heating vessel 10 and has a charge opening 14 as well as a discharge opening 15, which may likewise be sealed vacuum-tight or gas-tight. Also provided at the cooling vessel 11 is furthermore a closable valve opening 43, which likewise serves the purpose of venting.

[0027] Furthermore, the cooling vessel 11 has gas inlet and outlet openings 32, 33 and 34. The gas inlet opening 33 and the gas outlet opening 32 are in turn part of a line loop 17 and connected to one another via the line 29. The line loop 17 has a heat exchanger 26 and a pumping device 27 in addition to the shut-off devices 30 and 31. The heat exchanger 26 serves to cool gaseous cooling medium exhausted from the cooling vessel 11 , again especially an inert gas, such as nitrogen, argon and the like, via contact with a cooling medium, for example cooling water.

[0028] In accordance with the line loop 16, the line loop 17 is also provided with a fresh gas supply 28, which may likewise be sealed.

[0029] Similarly to the gas outlet 35 of the heating vessel 10, a gas removal opening 34 is provided in the cooling vessel 11 , said opening also being connected to the central pumping device 9 via corresponding exhaust gas lines 7.

[0030] The apparatus now works such that the material to be treated is charged into the heating vessel 10 through the charge opening 12. This material to be treated may, for example, be a crystalline polyethylene terephthalate from the preceding process step of the recycling of polyethylene terephthalate with a temperature of approximately 140 ⁰C. However, it is also possible to charge non-pre-heated or cold material into the heating vessel 10. When warm material is being charged, this can occur under vacuum conditions or in an inert gas atmosphere, such that the charge opening 12 has corresponding means for vacuum-tight or gas-tight connection of supply lines or transfer containers.

[0031] In the heating vessel 10, the charged plastic granules or the plastic particles are heated by through-passage of heated inert gas, especially heated nitrogen, to a desired temperature, for example a temperature of 200 ⁰C to 250 ⁰C. To this end, the inert gas in the line loop 16 is pumped such that the warm gas is injected via the gas inlet 25 into the lower region of the heating vessel 10, through the loose pile of plastic granules and is released at the gas outlet 24 from the heating vessel 10 into the line loop 16 again. This gas is then pumped through the line 23 and passes through the heating device 18, which, for example, may be an electrical heater, a gas heater or other heat source. In the heating device 18, the gas is heated up to corresponding temperatures in order that it may then finally be again blown through the gas inlet 25 into the heating vessel 10. The temperature in the heating vessel 10 and/or in the heating device 18 can be regulated or controlled by corresponding sensors and regulating or control circuits 18, such that altogether a precise and homogeneous temperature of the material to be processed in the heating vessel 10 can be guaranteed.

[0032] As soon as the material in the heating vessel 10 has the necessary temperature, it can be transferred in inert gas atmosphere or corresponding vacuum conditions to the vacuum dryer 1 , which follows the heating vessel 10. To this end, for example, the vacuum dryer 1 with its chamber 41 has to be rotated about the rotary axis 2, such that the charge opening 5 lies in the proximity of the discharge opening 13 of the heating vessel 10. The charge opening 5 and the discharge opening 13 of the heating vessel 10 can be connected together vacuum or gas-tight by corresponding coupling means, such that the material in the heating vessel 10 can be charged into the chamber 41 of the vacuum dryer.

[0033] Through the preheating in the heating vessel 10 of the plastic material to be treated, the vacuum dryer can begin immediately with the drying process and/or thermal treatment. Via the drive 4 in the form of an electric motor, the vacuum dryer 1 or the chamber 41 is set into corresponding rotation or swivelling movements. In the variant shown of embodiment of Fig. 1 with an upstream heating vessel 10, it is thus not necessary to heat the material first in the vacuum dryer 1 to the desired operating temperature in the range of, for example, 200⁰C to 250⁰C. Only possible heat losses during the treatment time need to be compensated for by an appropriate heating device. Since the necessary energy quantities require only a small amount of heating power, this heating device (not shown) can be preferably provided via heating mats that are simple to attach to the surface of the chamber 41.

[0034] Via the exhaust line 3 and 7, between which a corresponding shut-off valve 6 is provided, the chamber 41 of the vacuum dryer can be exhausted especially during the treatment of the plastic material, with the exhausted gas being transported across a filter 8 in order that dust particles and the like may be filtered out. Accordingly, during the entire treatment period, virtual vacuum conditions with very low pressures in the range of 0.01 mbar up to 1 mbar can be set and maintained .

[0035] After the requisite treatment in the vacuum dryer 1 , the vacuum dryer 1 is rotated such that that the charge opening 5 is arranged in the proximity of the chamber opening 14 of the cooling vessel 11 such that the corresponding means for vacuum-tight or gas-tight coupling of the charge opening 5 and the chamber opening 14 of the cooling vessel 11 can be connected together. [0036] The material in the vacuum dryer 1 is then transferred into the cooling vessel 11 , such that the vacuum dryer is immediately available again to receive new material to be treated, which in the meantime has again been heated in the heating vessel 10. In this way, very fast throughput of material with the inventive apparatus can be obtained, which is comparable as regards throughput rate and attainable efficiency with continuous in-line installations, wherein, however, at the same time, the precise and reproducible process conditions of a batch process can be set, since the various processes, such as heating and corresponding through-mixing in the dryer, have been separated. Cooling, too, no longer takes place in the dryer, but has been transferred to the cooling vessel 11. There, via the gas inlet opening 33, the cooling gas, especially inert gas, such as nitrogen or argon, is introduced into the lower region of the cooling vessel 11 , transported through the loosely piled plastic, whereby the cooling gas is heated and is released again into the line loop 17 at the gas discharge opening 32 . There, in the heat exchangers 26 arranged in the line 29, the gas is cooled by cooling water, which is fed through the heat exchanger, and the gas is pumped via the pumping device 27 into the cooling vessel 11 again. Here, too, a gas removal opening 34 is connected via the line 7 to the central pumping device 9 in order that the gas or the container may be pumped empty, for example after cooling. The gas removal opening 34 may also be sealed via a valve arrangement 37, such as the valve opening 43, which serves to vent the cooling vessel 11.

[0037] After the cooling, the container can be emptied via the discharge opening 15.

[0038] Fig. 2 shows a further embodiment of the inventive apparatus in which the apparatus of Fig. 1 has been further developed.

[0039] The apparatus of Fig. 2 essentially corresponds to that of Fig. 1 , such that the description and the reference symbols of the components are identical here and are not repeated. However, the two line loops 16 and 17 have each been extended by the subloops 38 and 39, which have a common heat exchanger 40. In this way, it is possible to effect direct heat exchange between the warm cooling medium or inert gas emanating from the cooling vessel 11 on one hand and the cool heating medium, again preferably inert gas, emanating from the heating vessel 10 in the heat exchanger 40. Thus, the heat recovered during the cooling process in the cooling vessel 11 can be partly reused to heat the plastic material in the heating vessel 10, a fact which leads to substantial energy saving. Although the invention has been described here on the basis of the preferred embodiments, it is clear that further variations and combinations are possible in accordance with the enclosed claims, which describe the scope of protection of the present invention.

Claims

1. Device for drying and/or thermal treatment of granular or particulate material, especially plastic, with a gas-tight sealable chamber (41) for the material under vacuum at elevated temperatures and a rotary axis (2) for rotating or swivelling the chamber, characterised by the fact that the jacket of the chamber (41) is formed as one wall.

2. Device in accordance with claim 1 , characterised by the fact that the chamber (41) has at least one gas inlet opening and/or exhaust opening.

3. Device in accordance with claim 1 or 2, characterised by the fact that the chamber (41) has at least two gas inlet and/or exhaust openings and/or means for through-feeding of gas, by means of which hot and/or cooling gases, especially inert hot and/or cooling gases may be passed through the chamber.

4. Device in accordance with any of claims 2 to 3, characterised by the fact that the gas inlet and/or exhaust openings are provided in the region of the rotary axis (2).

5. Device in accordance with any the previous claims, characterised by the fact that at least one, preferably exactly one charge and/or discharge opening (5) for the material to be dried and/or heat-treated is provided.

6. Device in accordance with claim 4, characterised by the fact that the charge opening (5) has means for vacuum-tight or gas-tight connection of a material line, a transfer vessel or a material store.

7. Device in accordance with any the previous claims, characterised by the fact that drive means (4) for rotating the chamber (41) are provided.

8. Device in accordance with any the previous claims, characterised by the fact that the chamber (41) has essentially a cylindrical or double cone shape, with the rotary axis for the tumbling motion running through the region of the edges of the jacket surface of the cylinder or for the rotary motion through the base of the double cone.

9. Vacuum dryer in accordance with any of the previous claims, characterised by the fact that at the outer surface of the chamber (41), electrical heating devices, especially heating mats, are at least partially arranged or arrangeable.

10. Apparatus for drying and/or thermal treatment of granular or particulate plastic material with a vacuum tumbling dryer (1) or vacuum double cone dryer or a device in accordance with any of the previous claims, characterised by the fact that a heating vessel (10) and/or a cooling vessel (11) is provided upstream and/or downstream.

11. Apparatus in accordance with claim 10, characterised by the fact that the upstream and/or downstream heating vessel (10) and/or cooling vessel (11) has means for vacuum-tight or gas-tight coupling to the vacuum tumbling dryer (1), the double cone dryer or a device in accordance with any of claims 1 to 9.

12. Apparatus in accordance with any of claims 10 to 11 , characterised by the fact that the upstream and/or downstream heating vessel (10) and/or cooling vessel (11) has at least one gas inlet and/or exhaust opening (24, 25, 30, 32, 33, 34), preferably at least two gas inlet and/or exhaust openings and/or means for through-feeding of gas, by means of which hot and/or cooling gases, especially inert hot and/or cooling gases may be passed through the chamber.

13. Apparatus in accordance with any of claims 10 to 12, characterised by the fact that at least one line loop (16, 17) for the hot and/or cooling gases is provided, said loop comprising conveyor means (19, 27), especially blower, and/or heat exchanger (26), especially with heating and/or cooling devices, and/or heating and/or cooling devices (18).

14. Apparatus in accordance with claim 13, characterised by the fact that for each heating and/or cooling vessel (10, 11) is provided a line loop (16, 17).

15. Apparatus in accordance with claim 13 or 14, characterised by the fact that a first line loop (16) for an upstream heating and/or cooling vessel (10) and a second line loop (17) for a downstream heating and/or cooling vessel (11) is provided, wherein first and second line loop are integrated into a heat exchanger (40), such that the heat extracted from a heating and/or cooling vessel (11), especially the downstream cooling vessel, serves in the heat exchanger (40) to heat the hot gas for the other heating and/or cooling vessel (10), especially an upstream heating vessel.

16. Apparatus in accordance with any of claims 10 to 15, characterised by the fact that at the heating and/or cooling vessels and/or the device, pumping or exhaust devices (9) are provided, especially with screen or filter devices (8).

17. Apparatus in accordance with any of claims 10 to 16, characterised by the fact that the material which is to be treated and is fed to the heating vessel and to the cooling vessel is passed by each other for heat exchange.

18. Method for the drying and/or thermal treatment of granular or particulate material, especially plastic under essentially vacuum conditions, characterised by the fact that in a first step, pre-heated material, is charged in the absence of air into a vacuum-tight or gas-tight sealable chamber (41) of a vacuum tumbling dryer (1) or double cone dryer or a device especially in accordance with any of claims 1 to 9, or non-pre-heated material is charged into a vacuum-tight or gas-tight sealable chamber (41) of a vacuum tumbling dryer (1) or vacuum double cone dryer or said device, especially in accordance with any of claims 1 to 9 and, after evacuation of the chamber, is heated by in-feeding and/or through-feeding of an inert hot gas and then mixed in a second step by movement of the chamber.

19. Method in accordance with claim 17, characterised by the fact that the method is a discontinuous (batch) method.

20. Method in accordance with any of claims 17 to 18, characterised by the fact that between first and second step and/or during the second step, gas is extracted from the chamber (41).

21. Method in accordance with any of claims 17 to 19, characterised by the fact that the material is heated before the first step and/or cooled after the second step, more precisely especially with a gaseous medium, especially inert gas, which is passed through the material, and/or through direct or indirect heat exchange between solid phases, solid and liquid phases, solid and gaseous phases or liquid and gaseous phases.

22. Method in accordance with any of claims 17 to 20, characterised by the fact that the heat generated during the cooling of the material after the second step is used at least in part to heat the material before the first step.

23. Method in accordance with any of claims 17 to 21 , characterised by the fact that it is performed in an apparatus in accordance with any of claims 10 to 16.

24. Method in accordance with any of claims 17 to 22, characterised by the fact that it is used for treating flakes, granules, particles, powder, general ground goods and the like made from plastic, especially polyester or polyethylene terephthalate (PET).

25. Method in accordance with any of claims 17 to 23, characterised by the fact that it is used as a sub-step in the recycling of polyethylene terephthalate (PET), especially for post-condensation.